1. Field of the Invention
The presented invention relates to a method and an apparatus to spray water confinement layer on the surface of workpiece during laser shock peening process, and forms a homogeneous water layer on the peening region. This method is suitable to form water layer on low curvature surface (curvature radius<50).
2. Background Art
Laser shock peening (LSP) is an advanced surface strengthening technology. With high power, high pressure, super speed and super strain rate, LSP technology has unmatched advantage over conventional methods. It can greatly improve the durability of metal, prevent the initiation of cracks, extend the life expectancy of workpieces and reduce the cost of maintenance. Since the beginning of the 21st century, USA has applied LSP technology to strengthen or repair turbine blades in fighter F101, F119 and F414.
In order to achieve the strengthen effect of LSP; a confinement layer should be applied on the peening surface. The thickness, material (Component and property) of the confinement layer directly affects the peening effect. Up to now, materials reported in literatures are: K9 glass, organic glass, silica gel, synthetic resin and water, etc. The glass like confinement layer has a great effect on upgrading shock power, but are only suitable on the flat surface. And it also has disadvantages such as frangibility and hard to clean. Silica gel and synthetic resin have a poor binding force with the target surface, and can hardly be reused. The advantages of the water confinement layer are: cheap, clean, recycle and can easily be applied to curved surface; the flowing water can also remove the solid particles produced by plasma Explosion. In LSP industry, water is the most commonly used material for confinement layer.
The typical industrial application of LSP is the laser shock peening process of the turbine blisk. For blades having curved surface, during the process, a programmable multi-axis workbench is used to adjust the motion and rotation of the blisk, to keep the laser beam perpendicular to the tangent plane of the peening point. Currently, the existing water confinement applying apparatus has a fixed water tap; the angle and the position of the water jet cannot be adjusted. During the peening process, if the water flow velocity is too big, a gap may form between the water layer and the concave surface of the blade. This phenomenon should be evaded, for laser will directly ablate the blade surface and cause undesired damage. If the water layer is too thick, it will negatively affect the LSP process. In order to achieve a perfect strengthen effect, only controlling the motion and position of the blisk is not enough, the direction of the water jet should also be optimized during the peening process.